It is known that, in order to improve emissions and combustion noise in internal combustion engines, a multiple fuel injection pattern can be used for each cylinder, such pattern being substantially composed by splitting the requested fuel quantity into several injections that may occur before and after the Top Dead Center of the piston. In a multi-injection pattern, the opening and closing of the injector needle generates a pressure wave that propagates along the fuel line. When a multi injection pattern is adopted, such fluctuations strongly affect the fuel delivery rate of the successive injection pulses and therefore may have a negative impact on emission levels and fuel consumption. In fact, the accuracy of the injected quantity in a multi-injection pattern is affected by the effect of the pressure wave in the fuel line: this wave represents the effect of a physical phenomenon known in hydraulics as water hammer.
A first approach known in the prior art to minimize such problem is the use of hydraulic systems designed and built specifically to compensate the pressure wave effect, for example by modifying physically the fuel line in order to decrease the wave pressure phenomena by introducing accurate holes or modifying the shape of the fuel accumulator. This approach is limited by the fact that it needs a specific modification of the fuel line for every engine system.
A second approach is the use of modified injectors that reduce the wave pressure effect using a specific damping volume inside the injector itself. However, this approach requires modifications to the injectors.
A further approach is to use a mapping of the effect of the pressure wave in order to apply a control strategy to compensate the injected quantity of the pulses that endure the wave pressure effect. This approach has the problem that it needs a different, complex map for every different engine system. In fact, the injected quantity in an injection belonging to a multi-injection pattern depends on the instantaneous value of the fuel line pressure and therefore the more accurate is the estimation of such value, the more accurate is the injection.
In view off the foregoing, at least one object is thus to obtain a reliable estimation of the instantaneous pressure value in the fuel line of a fuel injection system. At least a further object is to minimize the impact of the pressure fluctuations inside the fuel line on the injected quantity of each single pulse in a multi-injection pattern. At least another object is to provide the possibility of minimize the impact of the pressure fluctuations inside the fuel line without the need to modify mechanically the injector and/or the fuel line itself. At least another object is to provide an estimation of the pressure wave effect in a multi-injection pattern without using complex devices and by taking advantage from the computational capabilities of the Electronic Control Unit (ECU) of the vehicle. In addition, other objects, desirable features, and characteristics will become apparent from the subsequent summary and detailed description, and the appended claims, taken in conjunction with the accompanying drawings and this background.